The present invention relates to an information recording medium for reading and writing a large volume of information at high speed and with high precision, and more specifically to a magnetic recording medium for a magnetic disk, a substrate for the magnetic recording medium, and a magnetic storage apparatus, all having high performance and high reliability.
Recent years have seen a remarkable advance of sophisticated information society and multimedia combining a variety of forms of information have found a widespread use. One of information recording apparatus that support these developments is a magnetic recording disk drive. At present, efforts are being made to reduce the size of the magnetic recording disk drive while at the same time improving its recording density. The magnetic recording disk drive is also experiencing a rapid cost reduction. To realize high recording density of the magnetic recording disk, the following essential requirements must be met: (1) the distance between the magnetic recording disk and the magnetic head should be reduced; (2) coercivity of the medium should be increased; and (3) a signal processing method should be improved.
The magnetic recording medium among others requires an increased coercivity to realize a high density recording. In addition, to realize a recording density in excess of 10 Gb/in2 requires a reduction in a unit area in which magnetization reversal occurs. For that purpose, magnetic crystal grains must be reduced in size to a microfine level. Further, in addition to the grain size reduction of magnetic crystal grains, it is important in terms of thermal fluctuation to reduce the extent of grain size distribution. To meet these requirements, it has been proposed to provide a shield thin layer under a magnetic layer. One such example is U.S. Pat. No. 4,652,499.
In the related technology described above, there is a limitation to the control on the distribution of crystal grain size of the information recording magnetic layer and there are cases where fine grains and coarse grains coexist. The coexistence of fine and coarse grains poses problems when magnetization is reversed to record information. Small grains are influenced by leakage fields from surrounding magnetic crystal grains, while large grains interact with the surrounding magnetic crystal grains, so that ultra-high density magnetic recording in excess of 10 GB/inch2 may not be performed in stable condition.
To overcome these problems, an object of the present invention is to provide a substrate or platelike body suited for manufacturing a high performance magnetic recording medium. Another object of the present invention is to provide a high performance magnetic recording medium with little noise by refining the crystal grain size in a magnetic layer. Still another object of the present invention is to provide a magnetic recording medium with low noise, low thermal fluctuation and low thermal demagnetization by suppressing the dispersion of the crystal grain size distribution. A further object of the present invention is to provide a magnetic recording medium suited for high density recording by controlling the crystallographic orientation of the magnetic layer. A further object of the present invention is to provide a high density magnetic recording medium by reducing the magnetic interaction among magnetic grains to reduce the magnetization reversal unit for recording and erasure. A further object of the present invention is to provide a magnetic storage apparatus suited for high density magnetic recording.
The above objectives can be achieved by: forming an inorganic compound layer over the substrate, the inorganic compound layer including crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide and at least one kind of oxide lying as a non-crystalline phase in boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide; and forming a magnetic layer over the inorganic compound layer, the magnetic layer having a structure in which magnetic crystal grains are epitaxially grown from the surface of the crystal grains of the inorganic compound layer and a non-magnetic element or compound exists in grain boundaries between the magnetic crystal grains. Alternatively, it is possible to form the substrate from the inorganic compound and epitaxially grow the magnetic crystal grains of the magnetic layer over the substrate.
The crystal grains in the inorganic compound layer have a columnar structure with the crystallographic orientation, in which the columns extend in the layer thickness direction. It is preferred that the crystal grains have a uniform size when viewed in the in-plane direction of the inorganic compound layer, that the grain size distribution be a normal distribution, and that the standard deviation of the grain size distribution be 10% or less of the average grain size. The inorganic compound layer typically has a honeycomb structure in which hexagonal crystal grains are regularly arrayed two-dimensionally in the in-plane direction. When one crystal grain is considered, it is preferred that the number of crystal grains neighboring that one crystal grain in the in-plane direction be almost constant and the number of crystal grains surrounding (or adjoining) it two-dimensionally be between 5.7 and 6.3. Such a structure of the inorganic compound layer can be controlled by changing a ratio between a material forming a crystalline phase and a material forming a noncrystalline phase and a composition of the material forming the non-crystalline phase when the inorganic compound layer is formed.
The crystal grains in the substrate formed of the inorganic compound have at least near the surface of the substrate a columnar structure with a crystallographic orientation in which the columns extend in the direction of thickness of the substrate. The columnar structure is surrounded by a noncrystalline phase. It is preferred that in a plane near and parallel to the surface of the substrate the crystal grains be almost uniform in size, that their grain size distribution be a normal distribution and that the standard deviation of the grain size distribution be 10% or less of the average grain size. At least on the substrate surface, the substrate typically has a honeycomb structure in which hexagonal crystal grains are regularly arrayed two-dimensionally in a plane parallel to the substrate surface. When one crystal grain on the substrate surface is considered, it is preferred that the number of crystal grains neighboring that one crystal grain be almost constant and the number of crystal grains surrounding (or adjoining) it two-dimensionally be between 5.7 and 6.3. Such a structure of the substrate can be controlled by changing a ratio between a material forming a crystalline phase and a material forming a noncrystalline phase and a composition of the material forming the non-crystalline phase when the substrate is formed of an inorganic compound.
Over the substrate of inorganic compound or the inorganic compound layer having the characteristics described above, a magnetic layer is formed. In this case, it is advantageous that the magnetic crystal grains of the magnetic layer are epitaxially grown from the crystal grains of the inorganic compound substrate or inorganic compound layer. Surrounding the crystal grains of the crystal grains of the substrate or inorganic compound layer is a non-crystalline phase. The magnetic layer grows epitaxially over the underlying crystal grains and its epitaxial growth is suppressed over the non-crystalline phase. Because the growth mechanism of the magnetic layer over the crystal grains differs from that over the grain boundaries when the magnetic layer is grown, the orientation and structure of the magnetic layer change in the in-plane direction. This change leads to a change in magnetic characteristics, which is effective in reducing the magnetic interaction among the magnetic crystal grains.
To enable smooth epitaxial growth of the magnetic crystal grains in the magnetic layer, the difference between the lattice constant of the crystal grains in the inorganic compound substrate surface or the inorganic compound layer and the lattice constant of the magnetic crystal grains needs to be xc2x110% or less. Although it cannot be said definitively because the inner stress in the layer varies depending on the deposition apparatus and deposition conditions, if the mismatch in the lattice constant between the crystal grains of the inorganic compound layer (or substrate) and the magnetic crystal grains of the magnetic layer exceeds xc2x110%, a layer with an intermediate lattice constant may be provided between the inorganic compound layer (or substrate) and the magnetic layer to epitaxially grow the magnetic crystal grains. In this case, it is preferred that the intermediate layer have the same crystal structure as the magnetic layer and the inorganic compound layer (or substrate).
Epitaxially growing the magnetic crystal grains of the magnetic layer from the crystal grains in the inorganic compound layer (or inorganic compound substrate) allows the shape and grain size of the magnetic crystal grains to match those of the crystal grains of the inorganic compound layer (or substrate). This means that the grain size and shape of the magnetic crystal grains of the magnetic layer can be determined by the inorganic compound layer or the substrate.
As described above, the grain size in the in-plane direction of the crystal grains in the inorganic compound layer (or inorganic compound substrate) can be selected arbitrary by controlling the composition and manufacturing process. Further, because the grain size distribution of the crystal grains in the inorganic compound layer (or substrate) is significantly small and the crystal grains are arrayed regularly, it is possible to control the grain size distribution and grain arrangement of the magnetic crystal grains in the magnetic layer formed over the inorganic compound layer. As a result, noise, thermal fluctuation and thermal demagnetization resulting from the medium can be reduced substantially. The grain-to-grain distance in the inorganic compound layer (or substrate) can be changed easily by controlling the composition of the compound. The control of the grain-to-grain distance can reduce the magnetic interaction among the magnetic crystal grains. With the method described above, the magnetization reversal unit in the magnetic recording medium can be minimized.
The features of the present invention are summarized as follows.
A platelike body of the present invention, which comprises a substrate and an inorganic compound layer formed over the substrate, is characterized in that the inorganic compound layer includes crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the crystal grains and selected from silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide. This platelike body can be used to manufacture a magnetic recording medium by depositing a magnetic layer over the platelike body.
The crystal grains in the inorganic compound layer have a columnar structure with the columns extending in the layer thickness direction. It is preferred that the inorganic compound layer, when viewed along its surface, have 5.7 to 6.3 crystal grains on average surrounding each crystal grain. Typically, it has a honeycomb structure in which hexagonal crystal grains in the inorganic compound layer are arrayed regularly two-dimensionally in the in-plane direction.
The crystal grains in the inorganic compound layer can be made to have a grain size distribution whose standard deviation is 10% or less of the average grain size when viewed in the in-plane direction. Further, the crystal grains in the inorganic compound layer can be made to exhibit almost the same crystallographic orientation. The width of grain boundaries between the crystal grains in the inorganic compound layer can be set in the range between 0.5 nm and 2 nm. It is desired that the thickness of the inorganic compound layer be between 10 nm and 100 nm. The lower limit of the layer thickness is determined by the thickness at which the layer can be formed stably and the upper limit by the inner stress of the layer.
The inorganic compound substrate of this invention is characterized in that at least one kind of oxide selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide exists as a non-crystalline phase in grain boundaries between crystal grains, the crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide. When viewed along the surface of the inorganic compound substrate, it is preferred that 5.7 to 6.3 crystal grains on average surround one crystal grain. The crystal grains have at least near the surface of the substrate a columnar structure with the columns extending in the substrate thickness direction. This inorganic compound substrate can be used to manufacture a magnetic recording medium by depositing a magnetic layer over the substrate.
A magnetic recording medium of the invention, which includes a substrate, and an underlayer formed over the substrate and a magnetic layer formed directly over the underlayer or through a layer having a composition different from that of the underlayer, is characterized in that the underlayer is an inorganic compound layer which includes crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide, and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide.
It is preferred that the inorganic compound layer, when viewed in the in-plane direction, have 5.7 to 6.3 crystal grains on average surrounding each crystal grain. Typically, the inorganic compound layer has a honeycomb structure in which hexagonal crystal grains are regularly arrayed two-dimensionally in the in-plane direction. It is preferred that the crystal grains in the inorganic compound layer have a grain size distribution whose standard deviation is 10% or less of the average grain size when viewed in the in-plane direction. It is also preferred that the inorganic compound layer have a thickness of between 10 nm and 100 nm. The lower limit of the layer thickness is determined by the thickness at which the layer can be formed stably and the upper limit by the inner stress of the layer.
The magnetic layer can include magnetic crystal grains and non-magnetic element or compound present in grain boundaries between the magnetic crystal grains and have 5.7 to 6.3 magnetic crystal grains surrounding each magnetic crystal grain. The magnetic layer typically has a honeycomb structure in which hexagonal magnetic crystal grains are regularly arrayed two-dimensionally in the in-plane direction.
It is possible to have the magnetic crystal grains in the magnetic layer exist in areas corresponding to the crystal grains of the inorganic compound layer and have the non-magnetic element or compound exist in areas corresponding to the grain boundary phase of the inorganic compound layer. This can be realized by epitaxially growing the magnetic layer over the inorganic compound layer. The magnetic crystal grains in the magnetic layer can have a grain size distribution whose standard deviation is 10% or less of the average grain size when viewed in the in-plane direction, reflecting the structure of the inorganic compound layer. Similarly, the width of the grain boundaries between the magnetic crystal grains in the magnetic layer can be set in a range between 0.5 nm and 2 nm, reflecting the structure of the inorganic compound layer.
The magnetic recording medium of this invention, which includes a substrate, an underlayer formed over the substrate and a magnetic layer formed over the underlayer, is characterized in that the underlayer is an inorganic compound layer which includes crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide, and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide. The magnetic layer includes magnetic crystal grains made of cobalt or alloy having cobalt as its main element. The magnetic crystal grains of the magnetic layer can be epitaxially grown over the crystal grains of the underlayer.
The magnetic recording medium of this invention, which includes a circular disk substrate, an underlayer formed on the substrate and a magnetic layer formed over the underlayer, is also characterized in that the underlayer is an inorganic compound layer which includes crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide, and which has 5.7 to 6.3 crystal grains surrounding each crystal grain. The magnetic recording medium is also characterized in that between the underlayer and the magnetic layer is formed a thin layer which has a lattice constant differing by 10% or less from both the lattice constants of the crystal grains of the underlayer and the magnetic crystal grains of the magnetic layer. The magnetic crystal grains of the magnetic layer can be epitaxially grown over the crystal grains of the thin layer.
The magnetic layer can be a ferromagnetic layer of an alloy having cobalt as its main element and including at least two additional elements chosen from Cr, Pt, Ta, Nb, Pd, B, Si, Ti, V, Ru and Rh. The magnetic layer can have at least one of elements Cr, Ta and Nb precipitated within or near the grain boundaries between cobalt crystal grains.
The magnetic recording medium of this invention, which includes a substrate and a magnetic layer formed over the substrate, is characterized in that the substrate is an inorganic compound substrate in which at least one kind of oxide selected form silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide exists as a non-crystalline phase in grain boundaries between crystal grains, the crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide, and that the magnetic layer includes magnetic crystal grains made of cobalt or an alloy having Co as its main element.
The magnetic recording medium of this invention, which includes a substrate and a magnetic layer formed over the substrate, is characterized in that the substrate is an inorganic compound substrate in which at least one kind of oxide selected form silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide exists as a non-crystalline phase in grain boundaries between crystal grains, the crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide, and that the magnetic layer includes magnetic crystal grains made of cobalt or an alloy having Co as its main element and at least one kind of oxide lying as a noncrystalline phase in grain boundaries between magnetic crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide.
The magnetic recording medium of this invention, which includes a substrate, an underlayer formed over the substrate and a magnetic layer formed over the underlayer, is characterized in that the underlayer is an inorganic compound layer which includes crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide, and that the magnetic layer includes magnetic crystal grains made of Co or an alloy having Co as its main element and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the magnetic crystal grains and chosen from silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide. The magnetic crystal grains of the magnetic layer can be epitaxially grown over the crystal grains of the underlayer. The alloy for the magnetic layer with cobalt as a main element can be an alloy containing cobalt with at least one additional element selected from Pt, Pd, Gd, Tb, Dy, Ho, Cr, Sm, Nd and Y
It is preferred that the magnetic layer have the (11.0) plane of Co oriented parallel to the surface of the layer. It should be noted that this index representation uses a notation system of four index representation that omits a third term and that the omitted third term is a value satisfying (first term value)+(second term value)xe2x88x92(third term value)=0.
The substrate over which the underlayer is formed can use a glass substrate and a metal substrate formed of aluminum or aluminum alloy. Alternatively, a substrate having an NiP layer formed over glass, aluminum or aluminum alloy may be used.
The magnetic recording medium of this invention, which includes a circular disk substrate and a magnetic layer formed over the substrate, is also characterized in that the substrate is an inorganic compound substrate which includes crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide and at least one kind of oxide lying as a non-crystalline phase in grain boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide, and which has 5.7 to 6.3 crystal grains surrounding each crystal grain. The magnetic recording medium is also characterized in that between the substrate and the magnetic layer is formed a thin layer which has a lattice constant intermediate between the lattice constant of the crystal grains of the substrate and the lattice constant of the magnetic crystal grains of the magnetic layer. The difference in lattice constant between the underlayer and the magnetic layer can be mitigated by setting the lattice constant of the thin layer formed between the under layer and the magnetic layer in such a manner that its difference from both the lattice constant of the crystal grains of the underlayer and the lattice constant of the magnetic crystal grains of the magnetic layer is within 10%.
In a magnetic storage apparatus which comprises a magnetic recording medium, a magnetic recording medium driver for driving the magnetic recording medium, a magnetic head for writing into and reading from the magnetic recording medium, a head access system for driving the magnetic head, and a read/write signal processing system for processing the read/write signals to and from the magnetic head, the magnetic storage apparatus of this invention uses the magnetic recording medium that has been described above.
The present invention can provide a high performance magnetic recording medium with little noise and with low thermal fluctuation and low thermal demagnetization by suppressing the dispersion of crystal grain size in the magnetic layer and refining the crystal grains. As a result, ultrahigh density magnetic recording medium in excess of 20 GB/inch2 can be manufactured.
In this specification, when, as a result of the X-ray diffraction analysis on a specimen, a diffraction peak due to a crystal plane appears, i.e., the specimen is crystalline with respect to X-ray, the specimen is referred to as being crystalline (or in a crystalline phase). When no diffraction peak due to the crystal plane appears, the specimen is referred to as being amorphous or non-crystalline.